60 
DUTTON. 
and a corresponding one for the resistance offered by the 
viscosity, the integration for the entire mass might give ns 
a series of equipotential surfaces within the mass. The re¬ 
sultant force at any point of any equipotential surface would 
be normal to that surface. A similar construction may be 
applied to the adjoining denuded area, in which the defect 
of isostasy may be treated as so much mass with a negative 
algebraic sign. The resultants normal to the equipotential 
surfaces would, in this case, also have the negative sign. The 
effective force tending to produce movement would be the 
arithmetical sum of the normals or of a single resultant 
compounded of the two normals. From this construction 
we may derive a force which tends to push the loaded sea 
bottoms inward upon the unloaded land horizontally. 
This gives us a farce of the precise kind that is wanted to 
explain the origin of systematic plications. Long reflection 
and considerable analysis have satisfied me that it is sufficient 
both in intensity and in amount unless we assume for the 
mean viscosity of the superficial and subterranean masses 
involved in the movement a much greater value than I am 
disposed to concede. The result is a true viscous flow of the 
loaded littoral inward upon the unloaded continent. 
There may be in this proposition some degree of violence 
to a certain mental prejudice against the idea that the rock- 
ribbed earth, to which all our notions of stability and im¬ 
movableness are attached, can be made to flow. It may as¬ 
sist our efforts if we reflect upon the motion of the great ice 
sheet which covers Greenland. Here the masses involved 
are no greater than some masses of sediment. The specific 
gravity of ice is only about one-third that of the rock masses. 
The forces called into play to carry the glacier along hori¬ 
zontally do not seem to differ greatly in intensity or amount 
from the described forces, and the rigidity of the ice itself 
may not exceed the mean rigidity of the rock masses beneath 
the littoral. 
We may now proceed to inquire how this theory adjusts 
itself to the actual facts. And, firstly, where do systematic 
plications occur? 
